标志为bitset和uint64_t的并集

Question

Recently learned about unions in c++ and I come up with this in order to handle multiple flags represented by a single uint64_t,etc

union myflags_t
{
  uint64_t var;
  std::bitset<64> bits;

  myflags_t() { }
};

The alternative way I was using before was bit operations , specifically setting a bit and changing the nth bit to x .

Instead I can use

myflags_t flags;
flags.var = 0;
flags.bits[nth bit] = ...

My question is Which is faster the union or bit operations?

Also if it is faster to use the union why haven't I come across this before?

Edit: Removed memset (misunderstood and did not need it) The reason I'm using union is because later in the code I need to pass the variable as uint64_t Edit 2: Read over comments and I'm convinced that I'm using union wrong. The code creates undefined behaviour since unions are not meant for type punning. Going to close the question.

Answer 1

If you want to flip the nth bit you can do this.

#include <iostream>
#include <bitset>
#include <cstdint>

int main( void )
{
  uint64_t u64 = 1024;
  std::bitset <64> b64;

  b64 = u64;
  b64.flip(0);

  u64 = b64.to_ulong();

  std::cout << u64 << "\n";

  return 0;
}